This invention relates to a process for the recovery of soluble rhodium compounds from the organic phase of spent process streams in the preparation of 1,4-hexadiene from ethylene and 1,3-butadiene. 1,4-Hexadiene is a valuable monomer for use in manufacturing sulfur-curable EPDM rubber.
U.S. Pat. No. 3,845,154 (to W. J. Keller) describes a typical 1,4-hexadiene manufacturing process that would be benefited by the present invention. In the process of U.S. Pat. No. 3,845,154, ethylene and 1,3-butadiene are contacted in the presence of a rhodium catalyst in a poly (oxyethylene) ether solvent, usually at about 50.degree.-100.degree.C. and 100-700 psig. The reactor effluent contains 1,4-hexadiene, solvent, rhodium catalyst, various C.sub.8 -C.sub.12 by-products, and unchanged starting materials. Low-boiling materials (ethylene, 1,3-butadiene, and 1,4-hexadiene) are flashed off. The residual high-boiling liquid contains the polyether solvent, rhodium catalyst, and the high-boiling C.sub.8 -C.sub.12 by-products. A portion of this residual material is diverted, while the bulk is recycled to the reactor. The purpose of this diversion is to prevent accumulation of the undesirable high boilers. Valuable polyether solvent is recovered by water extraction of the diverted material.
Rhodium catalyst should be removed from that diverted portion of the liquid for economic reasons. This can be done, for example, by burning the high boiling by-products, but the low concentration of rhodium (e.g., 300- 1800 ppm) necessitates undesired handling of large volumes of liquid. In the event of a plant shutdown, it is particularly important to be able to recover rhodium from the whole process stream before the latter is discarded.
There is a need, therefore, for a simple method of recovery of soluble rhodium compounds from the reactor effluent.